Selective determination of pectinesterase activity in foodstuffs using a pervaporator coupled to an open-closed dynamic biosensing system

A selective automated method for monitoring pectinesterase (PE) activity in food is presented. The proposed method is based on indirect monitorisation of the methanol released by pectin demethoxylation catalysed by PE using an open-closed dynamic system coupled to a pervaporator. The use of analytical pervaporation as previous separation technique provides enough selectivity to determine PE in both fresh and processed foods without interferences. The biochemical system involved a two-step enzymic derivatisation reaction using alcohol oxidase (AOD) and horseradish peroxidase (POD) and fluorimetric monitorisation of the reaction product at lambda (ex) = 310 nm and lambda (em) = 415 nm. The method shows a linear range between 5 x 10(-5) and 0.2 U ml(-1), with a precision, expressed as R.S.D,, better than 4.8% and a sampling frequency of 4 h(-1). The usefulness of the method was tested by determining PE activity in natural and manufactured juices and applying the standard addition method with recoveries between 92.3 and 101.8%. (C) 2001 Elsevier Science B,V, Ah rights reserved.